A method further includes the following steps. Firstly, a three-dimensional picture under a generated background condition is generated, wherein the three-dimensional picture includes a three-dimensional object image. Then, a two-dimensional picture of the three-dimensional picture is captured, wherein the two-dimensional picture includes a two-dimensional object image of the three-dimensional object image. Then, an object region of the two-dimensional object image is recognized. Then, an exposed ratio of an exposed area of an exposed region of the object region to an object area of the object region is obtained. Then, whether the exposed ratio is greater than a preset ratio is determined. Then the exposed region is defined as the pick-and-place region when the exposed ratio is greater than the preset ratio.